U.S. patent application number 10/225318 was filed with the patent office on 2002-12-26 for light emitting device, semiconductor device, and method of manufacturing the devices.
Invention is credited to Miyazaki, Koichi.
Application Number | 20020195608 10/225318 |
Document ID | / |
Family ID | 18739310 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020195608 |
Kind Code |
A1 |
Miyazaki, Koichi |
December 26, 2002 |
Light emitting device, semiconductor device, and method of
manufacturing the devices
Abstract
The invention provides a light emitting device and a
semiconductor device each having improved characteristics by
preventing occurrence of a damage caused by contact of a tool. On a
substrate, an n-type semiconductor layer, an active layer, and a
p-type semiconductor layer are stacked. On the p-type semiconductor
layer, a p-side electrode is provided. The p-type semiconductor
layer has a projected portion for limiting current in
correspondence with a current injection area in the active layer. A
projected portion is formed on the surface of the p-side electrode
in correspondence with the projected portion for limiting current.
On the surface of the p-side electrode, a protective portion is
also provided in correspondence with the area other than the
current injection area in the active layer. The top face of the
protective portion is higher than that of the projected portion.
With the configuration, contact of a tool or the like with the
projected portion and its periphery can be prevented, so that the
projected portion and its periphery such as the projected portion
for limiting current and the current injection area in the active
layer can be prevented from being damaged.
Inventors: |
Miyazaki, Koichi; (Miyagi,
JP) |
Correspondence
Address: |
SONNENSCHEIN NATH & ROSENTHAL
P.O. BOX 061080
WACKER DRIVE STATION
CHICAGO
IL
60606-1080
US
|
Family ID: |
18739310 |
Appl. No.: |
10/225318 |
Filed: |
August 21, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10225318 |
Aug 21, 2002 |
|
|
|
09934058 |
Aug 21, 2001 |
|
|
|
Current U.S.
Class: |
257/79 ; 257/86;
438/22; 438/24 |
Current CPC
Class: |
H01L 33/387 20130101;
H01L 33/38 20130101 |
Class at
Publication: |
257/79 ; 438/22;
438/24; 257/86 |
International
Class: |
H01L 021/00; H01L
027/15; H01L 031/12; H01L 033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 21, 2000 |
JP |
P2000-249587 |
Claims
What is claimed is:
1. A light emitting device in which semiconductor layers including
an active layer are stacked on a substrate, wherein the active
layer has a current injection area into which a current is
injected, a projected portion is provided in correspondence with
the current injection area on the surface opposite to the
substrate, a projected protective portion is provided in
correspondence with an area other than the current injection area,
and the protective portion is projected so that its top face is
flush with or higher than that of the projected portion.
2. A light emitting device according to claim 1, wherein the
semiconductor layer has a projected portion for limiting current in
correspondence with the current injection area.
3. A light emitting device according to claim 1, wherein the
protective portion is made of a metal or an insulating
material.
4. A light emitting device according to claim 1, wherein the
semiconductor layer has a projected portion for protection in
correspondence with an area other than the current injection
area.
5. A light emitting device according to claim 1, further comprising
an electrode electrically connected to the semiconductor layer,
wherein the electrode serves as the surface of the projected
portion.
6. A light emitting device in which semiconductor layers including
an active layer are stacked on a substrate, wherein the active
layer has a current injection area into which a current is
injected, the semiconductor layer has a projected portion for
limiting current in correspondence with the current injection area,
a protective portion is provided in correspondence with an area
other than the current injection area on the surface opposite to
the substrate, and the protective portion is projected so that its
top face is flush with or higher than that of the area
corresponding to the current injection area, in the surface
opposite to the substrate.
7. A semiconductor device in which semiconductor layers are stacked
on a substrate, comprising a projected portion and a projected
protective portion having a top face flush with or higher than that
of the projected portion on the surface opposite to the
substrate.
8. A method of manufacturing a light emitting device, comprising: a
step of growing semiconductor layers including an active layer on a
substrate; a step of forming a projected portion for limiting
current in correspondence with the current injection area in the
active layer in the semiconductor layer, thereby forming a
projected portion in correspondence with the projected portion for
limiting current on the surface opposite to the substrate; and a
step of forming a protective portion projected so that its top face
is flush with or higher than that of the projected portion on the
surface opposite to the substrate in correspondence an area other
than the current injection area in the active layer.
9. A method of manufacturing a light emitting device according to
claim 8, wherein the protective portion is made of a metal or an
insulating material.
10. A method of manufacturing a light emitting device according to
claim 8, further comprising a step of forming a projected portion
for protection on the semiconductor layer in correspondence with
the area other then the current injection area in the active layer
by the same process as that of the projected portion for limiting
current.
11. A method of manufacturing a light emitting device, comprising:
a step of growing semiconductor layers including an active layer on
a substrate; a step of forming a projected portion for limiting
current on the semiconductor layer in correspondence with a current
injection area in the active layer; and a step of forming a
protective portion on the surface opposite to the substrate in
correspondence with the area other than the current injection area
in the active layer so that the top face of the protective portion
is flush with or higher than that of the area corresponding to the
current injection area, in the surface opposite to the
substrate.
12. A method of manufacturing a semiconductor device, comprising: a
step of growing semiconductor layers on a substrate; and a step of
forming a projected portion and a protective portion projected so
that its top face is flush with or higher than that of the
projected portion on the surface opposite to the substrate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a light emitting device and
a semiconductor device in each of which semiconductor layers are
stacked on a substrate, and a method of manufacturing the
devices.
[0003] 2. Description of the Related Art
[0004] At present, a semiconductor laser (laser diode: LD) is used
in various apparatuses such as optical disk drive, laser beam
printer, and copying machine. FIG. 1 shows an example of the
configuration of a conventional semiconductor laser. In the
semiconductor laser, an n-type cladding layer 113, an active layer
114, a first p-type cladding layer 115, an etching stop layer 116,
a second p-type cladding layer 117, and a p-side contact layer 118
are sequentially stacked on a substrate 111. By forming the second
p-type cladding layer 117 in a strip shape in correspondence with a
current injection area in the active layer 114, the current is
limited. On the surface opposite to the substrate 111 side, a
projected portion 123 is formed in correspondence with the second
p-type cladding layer 117.
[0005] In the conventional semiconductor laser shown in FIG. 1,
however, since the projected portion 123 is formed on the surface
in correspondence with the second p-type cladding layer 117, the
number of times a tool comes into contact with the projected
portion 123 and its peripheral area in a manufacturing process and
the like is large. It causes a problem such that the projected
portion 123 and its periphery, for example, the second p-type
cladding layer 117 and the current injection area in the active
layer 114 are vulnerable to damage. For example, in a case such
that a semiconductor laser is formed and carried to a measuring
device by using an adsorbent tool, despite of examinations of
improving the shape of a tool, controlling absorbing power of the
tool, and the like, the damage cannot be effectively prevented. Due
to this, the characteristics deteriorate.
SUMMARY OF THE INVENTION
[0006] The invention has been achieved in consideration of the
above problems and its object is to provide a light emitting device
and a semiconductor device each having improved characteristics by
preventing damage caused by contact of a tool, and a method of
manufacturing the devices.
[0007] According to an aspect of the invention, there is provided a
light emitting device in which semiconductor layers including an
active layer are stacked on a substrate, wherein the active layer
has a current injection area into which a current is injected, a
projected portion is provided in correspondence with the current
injection area on the surface opposite to the substrate, a
projected protective portion is provided in correspondence with an
area other than the current injection area, and the protective
portion is projected so that its top face is flush with or higher
than that of the projected portion.
[0008] According to the invention, there is also provided a light
emitting device in which semiconductor layers including an active
layer are stacked on a substrate, wherein the active layer has a
current injection area into which a current is injected, the
semiconductor layer has a projected portion for limiting current in
correspondence with the current injection area, a protective
portion is provided in correspondence with an area other than the
current injection area on the surface opposite to the substrate,
and the protective portion is projected so that its top face is
flush with or higher than that of the area corresponding to the
current injection area, in the surface opposite to the
substrate.
[0009] According to the invention, there is also provided a
semiconductor device in which semiconductor layers are stacked on a
substrate, including a projected portion and a projected protective
portion having a top face flush with or higher than that of the
projected portion on the surface opposite to the substrate.
[0010] A method of manufacturing a light emitting device according
to the invention includes: a step of growing semiconductor layers
including an active layer on a substrate; a step of forming a
projected portion for limiting current in correspondence with the
current injection area in the active layer in the semiconductor
layer, thereby forming a projected portion in correspondence with
the projected portion for limiting current on the surface opposite
to the substrate; and a step of forming a protective portion
projected so that its top face is flush with or higher than that of
the projected portion on the surface opposite to the substrate in
correspondence an area other than the current injection area in the
active layer.
[0011] Another method of manufacturing a light emitting device
according to the invention includes: a step of growing
semiconductor layers including an active layer on a substrate; a
step of forming a projected portion for limiting current on the
semiconductor layer in correspondence with a current injection area
in the active layer; and a step of forming a protective portion on
the surface opposite to the substrate in correspondence with the
area other than the current injection area in the active layer so
that the top face of the protective portion is flush with or higher
than that of the area corresponding to the current injection area,
in the surface opposite to the substrate.
[0012] Further another method of manufacturing a semiconductor
device according to the invention includes: a step of growing
semiconductor layers on a substrate; and a step of forming a
projected portion and a protective portion projected so that its
top face is flush with or higher than that of the projected portion
on the surface opposite to the substrate.
[0013] In each of the light emitting device and the semiconductor
device according to the invention, on the surface opposite to the
substrate of the device, the projected protective portion of which
top face is either flush with or higher than that of the projected
portion is provided. Consequently, the number of times a tool comes
into contact with the projected portion is reduced, thereby
preventing the projected portion and its periphery from being
damaged.
[0014] In another light emitting device according to the invention,
on the surface opposite to the substrate of the device, the
protective portion of which top face is either flush with or higher
than that of the area in the surface corresponding to the current
injection area is provided. Consequently, the number of times a
tool comes into contact with the surface corresponding to the
current injection area is reduced, thereby preventing the surface
corresponding to the current injection area and its periphery from
being damaged.
[0015] In each of the method of manufacturing the light emitting
device and the method of manufacturing the semiconductor device
according to the invention, on the surface opposite to the
substrate of the device, the projected protective portion of which
top face is either flush with or higher than that of the projected
portion is formed.
[0016] In another method of manufacturing the light emitting device
according to the invention, on the surface opposite to the
substrate of the device, the protective portion of which top face
is either flush with or higher than that of the area in the surface
corresponding to the current injection area is formed.
[0017] Other and further objects, features and advantages of the
invention will appear more fully from the following
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a cross section showing the configuration of a
conventional semiconductor laser.
[0019] FIG. 2 is a cross section showing the configuration of a
semiconductor laser according to a first embodiment of the
invention.
[0020] FIGS. 3A and 3B are cross sections showing a process of
manufacturing the semiconductor laser illustrated in FIG. 2.
[0021] FIGS. 4A and 4B are cross sections showing a manufacturing
process continued from FIG. 3B.
[0022] FIGS. 5A and 5B are cross sections showing a manufacturing
process continued from FIG. 4B.
[0023] FIG. 6 is a cross section showing a manufacturing process
continued from FIG. 5B.
[0024] FIG. 7 is a cross section showing the configuration of a
semiconductor laser according to a second embodiment of the
invention.
[0025] FIGS. 8A and 8B are cross sections showing a process of
manufacturing the semiconductor laser illustrated in FIG. 7.
[0026] FIG. 9 is a cross section showing a manufacturing process
continued from FIG. 8B.
[0027] FIG. 10 is a cross section showing a manufacturing process
continued from FIG. 9.
[0028] FIGS. 11A and 11B are cross sections showing a manufacturing
process continued from FIG. 10.
[0029] FIG. 12 is a cross section showing a manufacturing process
continued from FIG. 11B.
[0030] FIG. 13 is a cross section showing the configuration of a
semiconductor laser according to a third embodiment of the
invention.
[0031] FIG. 14 is a cross section showing a modification of the
invention.
[0032] FIG. 15 is a cross section showing another modification of
the invention.
[0033] FIG. 16 is a cross section showing another modification of
the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] Embodiments of the invention will be described in detail
hereinbelow with reference to the drawings.
[0035] [First Embodiment]
[0036] FIG. 2 shows the configuration of a semiconductor laser as a
light emitting device according to a first embodiment of the
invention. In the semiconductor laser, on one face side of a
substrate 11, semiconductor layers which are a buffer layer 12, an
n-type cladding layer 13, an active layer 14, a first p-type
cladding layer 15, an etching stop layer 16, a second p-type
cladding layer 17, and p-side contact layer 18 are sequentially
stacked in this order. The buffer layer 12 and the n-type cladding
layer 13 are n-type semiconductor layers corresponding to
semiconductor layers of a first conduction type. The first p-type
cladding layer 15, etching stop layer 16, second p-type cladding
layer 17, and p-side contact layer 18 are p-type semiconductor
layers corresponding to semiconductor layers of a second conduction
type.
[0037] The substrate 11, for example, has a thickness in the stack
direction (hereinbelow, simply called thickness) of 100 .mu.m and
is made of n-type GaAs in which an n-type impurity such as silicon
(Si) or selenium (Se) is doped. The buffer layer 12, for example,
has a thickness of 1 .mu.m and is made of n-type
Al.sub.0.3Ga.sub.0.7As mixed crystal in which an n-type impurity
such as silicon or selenium is doped. The n-type cladding layer 13,
for example, has a thickness of 1 .mu.m and is made of n-type
Al.sub.0.47Ga.sub.0.53As mixed crystal in which an n-type impurity
such as silicon or selenium is doped.
[0038] The active layer 14, for example, has a thickness of 80 nm
and is made of non-Al.sub.0.1Ga.sub.0.9As mixed crystal in which no
impurity is doped. The active layer 14 has a current injection area
into which a current is injected and a non-current injection area
other than the current injection area. The current injection area
functions as a light emitting area.
[0039] The first p-type cladding layer 15, for example, has a
thickness of 0.3 .mu.m and is made of p-type
Al.sub.0.47Ga.sub.0.53As mixed crystal in which a p-type impurity
such as zinc (Zn) is doped. The etching stop layer 16, for example,
has a thickness of 70 nm and is made of p-type
Al.sub.0.3Ga.sub.0.7As mixed crystal in which a p-type impurity
such as zinc is doped. The second p-type cladding layer 17, for
example, has a thickness of 1.2 .mu.m and is made of p-type
Al.sub.0.47Ga.sub.0.53As mixed crystal in which p-type impurity
such as zinc is doped.
[0040] At least a part of the etching stop layer 16 and the second
p-type cladding layer 17 are formed in a narrow strip shape (strip
shape elongated in the direction perpendicular to the drawing sheet
in FIG. 2), thereby forming a projected portion 17a for limiting
current. The projected portion 17a is used to regulate the current
injection area in the active layer 14, and the portion
corresponding to the projected portion 17a in the active layer 14
is the current injection area. On both sides of the projected
portion 17a, a current stop layer 19 having a thickness of 0.5
.mu.m, made of n-type GaAs in which an n-type impurity such as
silicon or selenium is doped is formed in correspondence with the
non-current injection area of the active layer 14.
[0041] The p-side contact layer 18 is formed by, for example,
diffusing a p-type impurity such as zinc and has a first diffusion
area 18a made of p-type GaAs and a second diffusion area 18b made
of p-type Al.sub.0.47Ga.sub.0.53As mixed crystal. The second
diffusion area 18b is, as will be described in a manufacturing
method hereinlater, an area formed by diffusing a p-type impurity
into a part of the second p-type cladding layer 17. The thickness
of the p-side contact layer 18 is, for example, 1 .mu.m.
[0042] The semiconductor laser has an n-side electrode 21 on the
side opposite to the one face of the substrate 11. The n-side
electrode 21 has, for instance, a structure in which an alloy layer
of gold and germanium (Ge), a nickel (Ni) layer, and a gold (Au)
layer are stacked sequentially on the substrate 11 and are alloyed
by heat treatment. The n-side electrode 21 is electrically
connected to an n-type semiconductor layer via the substrate 11. On
the other hand, a p-side electrode 22 is provided on the p-side
contact layer 18. The p-side electrode 22 has, for example, a
structure in which a titanium (Ti) layer, a platinum (Pt) layer,
and a gold layer are stacked sequentially on the p-side contact
layer 18 and are alloyed by heat treatment. The p-side electrode 22
is electrically connected to a p-side semiconductor layer. The
p-side electrode 22 corresponds to an example of "electrode" of the
invention.
[0043] On the surface of the p-side electrode 22, that is, on the
surface opposite to the substrate 11 of the semiconductor laser, a
projected portion 23 is formed in correspondence with the current
injection area in the active layer 14. The projected portion 23 is
formed in correspondence with the projected portion 17a from a
manufacture viewpoint and has a strip shape elongated in the same
direction as that of the projected portion 17a. The p-side
electrode 22 serves as the surface of the projected portion 23. The
projected portion 23 does not have to perfectly coincide with the
current injection area in the active layer 14. For example, as
shown in FIG. 2, the projected portion 23 may be provided in an
area slightly wider than the current injection area. On the
contrary, it may be provided in an area slightly narrower than the
current injection area. That is, it may be provided in relation
with the current injection area.
[0044] On the surface of the p-side electrode 22, that is, on the
surface opposite to the substrate 11 of the semiconductor laser,
projected protective portions 24 are formed in correspondence with
the non-current injection areas in the active layer 14. In the
embodiment, for example, the protective portions 24 extend in the
same direction as that of the projected portion 23 and are formed
on both sides of the projected portion 23. The protective portions
24 are made of, for example, a metal such as gold (Au) or an
insulating material such as silicon dioxide (SiO.sub.2) or silicon
nitride (Si.sub.3N.sub.4). The top face of the protective portion
24 is either flush with or higher than that of the projected
portion 23, thereby preventing contact of a tool or the like with
the projected portion 23. The protective portion 24 does not have
to perfectly coincide with the non-current injection area of the
active layer 14. For example, as shown in FIG. 2, the protective
portion 24 may be provided in a part of an area corresponding to
the non-current injection area or in an area slightly wider than
the non-current injection area. That is, it may be provided in
relation with the non-current injection area.
[0045] A pair of side faces facing in the extending direction of
the second p-type cladding layer 17, of the semiconductor laser
serve as resonator end faces. On the pair of resonator end faces, a
pair of not-illustrated reflector films are formed. One of the
reflector films is made of, for example, aluminum oxide
(Al.sub.2O.sub.3) and is adjusted so as to have a low reflectance.
The other reflector film is constructed by, for example,
alternately stacking an aluminum oxide film and an amorphous
silicon layer so as to have a high reflectance. With the
configuration, light generated by the active layer 14 is amplified
by being reflected between the pair of reflector films and the
amplified light is emitted as a laser beam from the reflector film
on the low reflectance side.
[0046] The semiconductor laser having such a configuration can be
manufactured as follows.
[0047] FIGS. 3A and 3B to FIG. 6 show a method of manufacturing the
semiconductor laser according to the embodiment in accordance with
the order of processes. First, as shown in FIG. 3A, for example, on
one face of the substrate 11 made of n-type GaAs having a thickness
of 450 .mu.m, the buffer layer 12 made of n-type
Al.sub.0.3Ga.sub.0.7As mixed crystal, the n-type cladding layer 13
made of n-type Al.sub.0.47Ga.sub.0.53As mixed crystal, the active
layer 14 made of non-Al.sub.0.1Ga.sub.0.9As mixed crystal, the
first p-type cladding layer 15 made of p-type
Al.sub.0.47Ga.sub.0.53As mixed crystal, the etching stop layer 16
made of p-type Al.sub.0.3Ga.sub.0.7As mixed crystal, and the second
p-type cladding layer 17 made of p-type Al.sub.0.47Ga.sub.0.53As
mixed crystal are sequentially grown by MOCVD (Metalorganic
Chemical Vapor Deposition).
[0048] As shown in FIG. 3B, for example, a not-illustrated mask
layer is formed on the second p-type cladding layer 17 and the
second p-type cladding layer 17 is selectively removed by using the
etching stop layer 16 by reactive ion etching (RIE). By the
operation, at least a part of the second p-type cladding layer 17
and the etching stop layer 16 are formed in a narrow strip shape in
correspondence with the current injection area in the active layer
14, thereby forming the projected portion 17a. After that, the
not-illustrated mask layer is removed.
[0049] As shown in FIG. 4A, for example, on the first p-type
cladding layer 15 and the projected portion 17a, the current stop
layer 19 made of n-type GaAs is grown by MOCVD. In this case, the
thickness of the current stop layer 19 to be grown is set to be a
sufficient thickness also including the amount of forming the
p-side contact layer 18 by diffusing a p-type impurity in a part of
the current stop layer 19 in a process which will be described
hereinlater. After that, for example, by using the lithography
technique, an upper part 19a of the projected portion corresponding
to the projected portion 17a in the grown current stop layer 19 is
selectively removed by RIE.
[0050] After selectively removing the current stop layer 19, as
show in FIG. 4B, for example, a p-type impurity such as zinc is
diffused in an upper part of the current stop layer 19 and in an
upper part of the second p-type cladding layer 17. A first
diffusion area 18a in the p-side contact layer 18 is formed in the
upper part of the current stop layer 19 and a second diffusion area
18b of the p-side contact layer 18 is formed in the upper part of
the second p-type cladding layer 17.
[0051] After forming the p-side contact layer 18, as shown in FIG.
5A, for example, the other face of the substrate 11 is lapped to
adjust the thickness of the substrate 11 to 100 .mu.m, an alloy
layer of gold and germanium, a nickel layer, and a gold layer are
sequentially vapor-deposited on the other face and are subjected to
heat treatment, thereby forming the n-side electrode 21. On the
p-side contact layer 18, for example, a titanium layer, a platinum
later, and a gold layer are sequential vapor-deposited and
subjected to heat treatment, thereby forming the p-side electrode
22. Since the projected portion is formed on the surface of the
p-side contact layer 18 in correspondence with the projected
portion 17a, also on the surface of the p-side electrode 22, the
projected portion 23 is formed in correspondence with the projected
portion 17a.
[0052] After forming the n-side electrode 21 and the p-side
electrode 22, as shown in FIG. 5B, for example, a resist film 31 is
applied on the p-side electrode 22, exposed by using a not-shown
mask, and developed, thereby forming a predetermined pattern. By
the operation, the projected portion 23 is covered with the resist
film 31.
[0053] After that, as shown in FIG. 6, on the p-side electrode 22,
for example, the protective portion 24 made of a metal or
insulating material is selectively formed by vapor deposition by
using the resist film 31. At this time, the top face of the
protective portion 24 is set to be either flush with or higher than
that of the projected portion 23. After forming the protective
portion 24, the resist film 31 is removed by, for example, an
organic solvent and a deposited layer 32 deposited on the resist
film 31 at the time of forming the protective portion 24 is
simultaneously removed. After that, the substrate 11 is shaped in a
predetermined size, and not-shown reflector films are formed on the
pair of resonator end faces facing each other in the extending
direction of the projected portion 17a. In such a manner, the
semiconductor laser shown in FIG. 2 is formed.
[0054] The semiconductor laser acts as follows.
[0055] In the semiconductor laser, when a predetermined voltage is
applied across the n-side electrode 21 and the p-side electrode 22,
the current is limited by the projected portion 17a, the current is
injected into the current injection area in the active layer 14,
and light is generated by recombination of electrons and holes. The
light is reflected between the not-illustrated pair of reflector
films to thereby carry out laser oscillation, and the resultant is
emitted as a laser beam to the outside. Since the protective
portion 24 is formed in correspondence with the non-current
injection area in the active layer 14 and the top face of the
protective portion 24 is either flush with or higher than the
projected portion 23, the number of times that a tool comes into
contact with the projected portion 23 and its periphery is small at
the time of manufacture, and the projected portion 23 and its
periphery, for example, the projected portion 17a, current
injection area in the active layer 14, and the like are prevented
from being damaged. Thus, improved characteristics and improved
quality are achieved.
[0056] According to the embodiment, on the surface opposite to the
substrate 11 of the semiconductor laser, the protective portions 24
each having the top face flush with or higher than that of the
projected portion 23 are formed. Consequently, the number of times
that a tool comes into contact with the projected portion 23 and
its periphery at the time of manufacture can be reduced. The
projected portion 23 and its periphery, that is, projected portion
17a, current injection area in the active layer 14, and the like
are prevented from being damaged. Thus, improved characteristics
and improved quality are achieved. Moreover, improved appearance
yield can be obtained.
[0057] [Second Embodiment]
[0058] FIG. 7 shows the configuration of a semiconductor laser
according to a second embodiment of the invention. The
semiconductor laser has the same configuration, action, and effects
as those of the first embodiment except for the configuration of a
protective portion 44. The same components as those of the first
embodiment are designated by the same reference numerals and their
detailed description will not be repeated here.
[0059] The semiconductor laser has projected portions 47b for
protection formed by the second p-type cladding layer 17 and the
etching stop layer 16 on both sides of the projected portion 17a
via the current stop layer 19. The projected portions 47b are
formed in correspondence with the non-current injection areas in
the active layer 14 and extend, for example, in the same direction
as the projected portion 17a. The current stop layer 19 is
interposed between the projected portion 47b and the first
diffusion area 18a in the p-side contact layer 18 to thereby
prevent the passage of a current via the projected portion 47b.
[0060] The protective portion 44 is formed in correspondence with
the projected portion 47b from a manufacture viewpoint. In the
second embodiment, the p-side electrode 22 serves as the surface of
the protective portion 44. Except for this, the protective portion
44 is the same as the protective portion 24 in the first
embodiment.
[0061] The semiconductor laser having such a configuration can be
manufactured as follows.
[0062] FIGS. 8A and 8B to FIG. 12 show a method of manufacturing
the semiconductor laser according to the second embodiment in
accordance with the order of processes. First, in a manner similar
to the first embodiment, on one face of the substrate 11, the
buffer layer 12, n-type cladding layer 13, active layer 14, first
p-type cladding layer 15, etching stop layer 16, and second p-type
cladding layer 17 are sequentially grown (refer to FIG. 3A).
Subsequently, as shown in FIG. 8A, for example, the second p-type
cladding layer 17 is selectively removed by using the etching stop
layer 16 by RIE to thereby form the projected portion 17a and the
projected portion 47b in the same process.
[0063] Subsequently, as shown in FIG. 8B, for example, on the first
p-type cladding layer 15, projected portion 17a, and projected
portion 47b, in a manner similar to the first embodiment, the
current stop layer 19 made of n-type GaAs is grown. In this case as
well, in a manner similar to the first embodiment, the thickness of
the current stop layer 19 to be grown is set to be a sufficient
thickness also including the amount of forming the p-side contact
layer 18 by diffusing a p-type impurity in a part of the current
stop layer 19 in a process which will be described hereinlater.
After growing the current stop layer 19, for example, as shown in
FIG. 9, a resist film 33 is applied on the current stop layer
19.
[0064] After that, for example, as shown in FIG. 10, by using a
mask 34, the portion projected in correspondence with the projected
portion 17a in the resist film 33 is selectively exposed and
developed, thereby forming an opening 33a in the resist film 33 in
correspondence with the projected portion 17a as shown in FIG. 11A.
After forming the opening 33a in the resist film 33, as shown in
FIG. 11B, for example, by using the resist film 33 as a mask, an
upper part of the portion projected in correspondence with the
projected portion 17a in the current stop layer 19 is selectively
removed by RIE.
[0065] After selectively removing the current stop layer 19, as
show in FIG. 12, for example, a p-type impurity such as zinc is
diffused in an upper part of the current stop layer 19 and in an
upper part of the projected portion 17a. By the operation, the
first diffusion area 18a of the p-side contact layer 18 is formed
in the upper part of the current stop layer 19 and the second
diffusion layer 18b of the p-side contact layer 18 is formed in the
upper part of the projected portion 17a.
[0066] After forming the p-side contact layer 18, for example, in a
manner similar to the first embodiment, the other face of the
substrate 11 is lapped to form the n-side electrode 21, and the
p-side electrode 22 is formed on the p-side contact layer 18. Since
the projected portions are formed on the surface of the p-side
contact layer 18 in correspondence with the projected portion 17a
and the projected portion 47b, the projected portion 23 is formed
on the surface of the p-side electrode 22 in correspondence with
the projected portion 17a, and the projected protective portion 44
is formed in correspondence with the projected portion 47b. In the
embodiment, as shown in FIG. 11B, the upper part of the current
stop layer 19 is removed in correspondence with the projected
portion 17a, so that the top face of the protective portion 44 is
formed so as to be projected more than the projected portion
23.
[0067] After that, the substrate 11 is shaped in a predetermined
size, and no-shown reflector films are formed on the pair of
resonator end faces facing each other in the extending direction of
the projected portion 17a. In such a manner, the semiconductor
laser shown in FIG. 7 is formed.
[0068] [Third Embodiment]
[0069] FIG. 13 shows the configuration of a semiconductor laser
according to a third embodiment of the invention. The semiconductor
laser has a plurality of (four in this case) laser oscillating
units 50a, 50b, 50c, and 50d arranged via isolation grooves 51 on
the common substrate 11. Each of the laser oscillating units 50a,
50b, 50c, and 50d has substantially the same configuration as that
of the semiconductor laser of the first embodiment except for a
protective portion 54. Specifically, on one face side of the
substrate 11, the buffer layer 12, n-type cladding layer 13, active
layer 14, first p-type cladding layer 15, etching stop layer 16,
second p-type cladding layer 17, and p-side contact layer 18 are
stacked in this order, the second p-type cladding layer 17 is
formed in a narrow strip shape which is the projected portion 17a,
and the current stop layer 19 is formed on both sides of the
projected portion 17a. On the other face side of the substrate 11,
the n-side electrode 21 shared by the laser oscillating units 50a,
50b, 50c, and 50d is formed. On the p-side contact layer 18, the
p-side electrode 22 is formed for each of the laser oscillation
units 50a, 50b, 50c, and 50d. The same components as those of the
first embodiment are designated by the same reference numerals and
their detailed description will not be repeated.
[0070] In each isolation groove 51, a buried layer 52 made of, for
example, an insulating material is formed. The protective portion
54 made of, for example, an insulating material, is formed on the
buried layer 52. On the surface of the p-side electrode 22 of each
of the laser oscillating units 50a and 50d positioned on both ends,
the protective portion 54 is formed in correspondence with the
non-current injection area on the outer side of the active layer
14. The protective portion 54 is not limited to the non-current
injection area but may be provided in correspondence with an area
other than the current injection area in the active layer 14. The
other configuration of the protective portion 54 is the same as
that of the protective portion 24 in the first embodiment. The
protective portion 54 may be provided only on the buried layer
52.
[0071] The semiconductor laser having such a configuration can be
manufactured in a manner similar to the first embodiment, similarly
acts, and produces similar effects. Although the case where each of
the laser oscillating units 50a, 50b, 50c, and 50d has the
configuration substantially the same as that of the first
embodiment has been described in the third embodiment, it is also
possible to use, as the configuration of the laser oscillating
unit, substantially the same configuration of the semiconductor
laser of the second embodiment, and form the protective portion
also on the isolation groove.
[0072] Although the invention has been described by the
embodiments, the invention is not limited to the foregoing
embodiments but can be variously modified. For example, the case of
providing the projected portion 23 on the surface of the p-side
electrode 22, that is, on the surface opposite to the substrate 11
of the semiconductor laser in correspondence with the current
injection area in the active layer 14 has been described in the
embodiments. However, the projected portion 23 may not be always
provided. For example, as shown in FIG. 14, there is a case such
that the protective portion 44 is provided in a wide range and no
projected portion is formed in the surface in correspondence with
the projected portion 17a. In this case, by forming the
semiconductor laser in such a manner that the top face of the
protective portion 44 is flush with or higher than the area in the
surface corresponding to the current injection area of the active
layer 14, the same effects as those of the foregoing embodiments
can be obtained.
[0073] For example, as shown in FIG. 15 or 16, there is a case that
the projected portion is not formed on the surface in
correspondence with the projected portion 17a according to the
structure of the light emitting device. The projected portion 17a
may be projected on the side opposite to the substrate 11 of the
semiconductor laser, from the flat face of the substrate 11 and a
p-type semiconductor layer (flat face of the first p-type cladding
layer 15 in FIGS. 15 and 16). In this case as well, by making the
top face of the protective portion 24 flush with or higher than the
area in the surface corresponding to the current injection area in
the active layer 14, effects similar to those of the foregoing
embodiments can be obtained and the reliability can be
increased.
[0074] Further, in the foregoing embodiments, the cases where the
protective portions 24 and 44 extend in the same direction as the
projected portion 23 and are provided on both sides of the
projected portion 23 have been described. The protective portion
may be of any shape and may be provided only one of the sides of
the projected portion 23.
[0075] In addition, in the foregoing embodiments, concrete examples
of the configuration of the semiconductor laser have been
described. The invention, however, can be similarly applied to
semiconductor lasers having other structures. Although the case of
using the n type as the first conduction type and using the p type
as the second conduction type has been described in the foregoing
embodiments, the invention can be similarly applied to a case where
the p type is used as the first conduction type and the n type is
used as the second conduction type.
[0076] Further, although concrete examples of the materials
constructing the semiconductor laser have been described in the
embodiments, the invention can be widely applied to cases of using
other semiconductor materials such as III-V compound
semiconductors, III-V nitride compound semiconductors, and II-VI
compound semiconductors.
[0077] In addition, although the case where the semiconductor
layers are grown by MOCVD has been described in the embodiments,
they may be grown by other methods such as molecular beam epitaxy
(MBE).
[0078] Further, although the semiconductor laser has been
concretely described in the foregoing embodiments, the invention
can be also applied to other light emitting devices such as light
emitting diode (LED). The invention can be also applied to a
semiconductor device in which semiconductor layers are stacked on a
substrate and a projected portion is formed on the surface opposite
to the substrate of the device. For example, by providing a
protective portion projected so that its top face is flush with or
higher than the top face of the projected portion on the surface
opposite to the substrate of the device, effects similar to those
of the foregoing embodiments can be obtained. Specifically, when a
projected portion is formed by a gate electrode on the surface
opposite to the substrate in an FET (Field Effect Transistor) such
as HEMT (High Electron Mobility Transistor), a protective portion
projected so that its top face is flush with or higher than the top
face of the gate electrode may be provided so as to sandwich the
gate electrode.
[0079] In the light emitting device and the method of manufacturing
the same according to the invention as described above, on the
surface opposite to the substrate of the device, the protective
portion projected so that its top face is flush with or higher than
that of the projected portion is provided, or the protective
portion projected so that its top face is flush with or higher than
that of an area in the surface corresponding to the current
injection area is provided. Consequently, the number of times a
tool comes into contact with the projected portion and its
periphery or the area in the surface corresponding to the current
injection area and its periphery at the time of manufacture can be
reduced. Thus, the projected portion and its periphery or the area
in the surface corresponding to the current injection area and its
periphery and, particularly, the current injection area can be
prevented from being damaged. Consequently, improved
characteristics and improved quality can be achieved. The
appearance yield can be also improved.
[0080] In the semiconductor device and the method of manufacturing
the semiconductor device according to the invention, the protective
portion projected so that its top face is flush with or higher than
that of the projected portion is provided on the surface opposite
to the substrate of the device. Consequently, the number of times a
tool comes into contact with the projected portion and its
periphery can be reduced. Thus, the projected portion and its
periphery can be prevented from being damaged. When the projected
portion and its periphery relate to the characteristics,
particularly improved characteristics can be achieved. Also, the
appearance yield can be also improved.
[0081] Obviously many modifications and variations of the present
invention are possible in the light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims the invention may be practiced otherwise than as
specifically described.
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